build a machine that can go underground

Could you have them build a machine that can travel underground and make tunnels that can be walked in?That would be a neat episode to watch.It would have to be no bigger that 8ft long and 5ft high,and have a drill type thing on the front to dig.and make it so it can't be collapsed or melted.I like that idea because i don't think anyone has done it yet and if they are good enough technians and mechanics they should be able to do it.There will have to be some setbacks though and some weaknesses to the machine,but not major technical weaknesses.

Answers

Ok, I'm picturing something between the hallway-scouring machine in
the movie "Labryinth" and the giant tunneling machines that built the
Chunnel. (By the way, they left one down there- maybe we could
hot-wire it?) The only drawback to this challenge is purely from a TV
production point of view: How would you film it??? With both machines
working underground, the TV show would end up looking a lot like the
French waiting for the Trojan Rabbit in Monty Python's "Holy Grail. So
maybe this would work after all!